1. Field of the Invention
The present invention relates to a method and apparatus for transmitting data in a next-generation mobile communication system. More particularly, the present invention relates to a method and apparatus for interleaving data in a mobile communication system.
2. Description of the Related Art
With respect to mobile communication systems, intensive research is being conducted on Orthogonal Frequency Division Multiple Access (OFDMA) and Single Carrier-Frequency Division Multiple Access (SC-FDMA) as schemes useful for high-speed data transmission in a wireless channel.
At present, 3rd Generation Partnership Project (3GPP), the standards group for asynchronous cellular mobile communications, is studying Long Term Evolution (LTE) or the Evolved Universal Terrestrial Radio Access (E-UTRA) system, which is the next-generation mobile communication system, based on the above-stated multiple access schemes.
A multiple access scheme generally allocates and manages time-frequency resources on which it will carry data or control information for each user separately so that they do not overlap each other, i.e., they keep orthogonality, thereby distinguishing data or control information for each user. For control channels, the multiple access scheme can additionally allocate code resources, thereby distinguishing control information for each user.
FIG. 1 is a diagram illustrating time-frequency resource and subframe structure for transmitting data or control information on an uplink in a conventional 3GPP LTE system. In FIG. 1, the horizontal axis represents a time domain and the vertical axis represents a frequency domain.
Referring to FIG. 1, the minimum transmission unit in the time domain is an SC-FDMA symbol. Nsymb SC-FDMA symbols 102 constitute one slot 106 and 2 slots constitute one subframe 100. The number Nsymb of SC-FDMA symbols is variable according to a length of a Cyclic Prefix (CP) that is added to every SC-FDMA symbol for prevention of inter-symbol interference. For example, Nsymb=7 for a normal CP, and Nsymb=6 for an extended CP.
A length of the slot is 0.5 ms and a length of the subframe is 1.0 ms. The minimum transmission unit in the frequency domain is a subcarrier, and the entire system transmission band is composed of a total of NBW subcarriers 104. NBW is a value that is in proportion to the system transmission band. For example, NBW=600 for the 10-MHz transmission band.
In the time-frequency domain, the basic unit of resources is a Resource Element (RE) 112, that can be indicated by a subcarrier index k and an SC-FDMA symbol index 1, wherein 1 has a value between 0 114 and Nsymb−1 116. A Resource Block (RB) 108 is defined by Nsymb consecutive SC-FDMA symbols 102 in the time domain and NRB consecutive subcarriers 110 in the frequency domain. Therefore, one RB 108 is composed of Nsymb*NRB REs 112. Resources for data transmission are scheduled in the time domain by an Evolved Node B (ENB), also known as a Base Station (BS), in units of 2 consecutive RBs.
FIG. 2 is a diagram illustrating a subframe structure for Nsymb=7 in a conventional 3GPP LTE system.
Referring to FIG. 2, a subframe 202, which is a basic transmission unit of the uplink, has a 1-ms length, and one subframe is composed of two 0.5-ms slots 204 and 206. The slots 204 and 206 are each composed of a plurality of SC-FDMA symbols 211˜224. In an example of FIG. 2, in one subframe 202, data is transmitted in SC-FDMA symbols indicated by reference numerals 211, 212, 213, 215, 216, 217, 218, 219, 220, 222, 223 and 224, and pilots (also referred to as a Reference Signal (RS)) are transmitted in SC-FDMA symbols indicated by reference numerals 214 and 221. Therefore, for one subframe, there are a total of 12 SC-FDMA symbols for data transmission. The pilot, composed of a predefined sequence, is used for channel estimation for coherent demodulation at the receiver. The number of SC-FDMA symbols for control information transmission, the number of SC-FDMA symbols for RS transmission, and their positions in the subframe are given herein by way of example, and these are subject to change according to the system operation.
The LTE system employs turbo coding as an error correcting coding or channel coding method for increasing reception reliability of data. For optimized realization, the maximum size Z of an input bit stream (hereinafter referred to as ‘code block’) of a turbo code may not exceed 6144 bits. Therefore, when the amount of desired transmission data is greater than 6144 bits, the LTE system segments the desired transmission data into a plurality of code blocks, and then channel-codes the code blocks individually. It is characterized that a size of the code block is a multiple of 8. The channel-coded code blocks each undergo rate matching on a code block by code block basis, so that their sizes are adjusted to be matched with the amount of allocated resources. There is an additional need for an interleaving operation for making the code blocks be robust against a burst error on a wireless transmission path, and a modulation operation for increasing the spectral efficiency. The interleaving operation combines a plurality of code blocks and processes them, and the modulation operation is performed on the code blocks individually, thereby preventing the possible case where symbols of different code blocks constitute one modulation symbol.
However, a definition of the detailed interleaving operation is not given in the LTE system.